A precise study of solar energetic particles provides an important basis to understand their acceleration
and propagation in the interplanetary space. A specific interest is paid to solar protons
possessing energy high enough, so that they can induce an atmospheric cascade in the Earth’s
atmosphere, whose secondary particles reach the ground, eventually being registered by groundbased
detectors e.g. neutron monitors. This particular class of events is called ground-level
enhancements (GLEs). The solar cycle 23 provided several strong GLEs. The first strong GLE
event of the cycle was observed on 14 July 2000 (the Bastille day event), while the last was
observed on 13 December 2006. In addition, the period of late October - early November 2003
was characterized by strong cosmic ray variability and a sequence of three GLEs (the so-called
Halloween GLEs) was registered, which is the focus of this study. Here, we performed a precise
analysis of neutron monitor records and derived the spectral and angular characteristics of the
solar energetic particles during the Halloween GLEs. We modeled the particle propagation in the
Earth’s magnetosphere and atmosphere using a verified NM yield function computed at several
altitudes above the sea level. The solar protons spectra and pitch angle distributions were obtained
in their dynamical development throughout the events. We briefly discuss the revealed features of
the Halloween events.